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On 7 Mar 2003 at 13:17, Shad Laws wrote: > You're talking about distances in different directions. No, I'm not, but perhaps I haven't explained myself well. I just meant that if there were triggering errors in position, those errors w would tend to be some distance which would become a smaller percentage of the circumference as the radius became larger. > The radius effects how much a given tolerance effects timing. In > other words, if magnet placement is 0.001" off with a radius of 3/8" > (kinda like Pertronix), that's _16_ times worse than being 0.001" off > with a radius of 6" (kinda like a flywheel). That's just one of the kinds of errors I was talking about. > The actual distance between the sensor and the magnets is on the order of > ~0.050" or so. Crank endplay can be roughly 5-10% of that measurement, > which is significant. However, distance effects the _strength_ of the > hall-effect pulse. But, you don't time based on the strength of the pulse. You > time by finding a transition point in the primary hall effect voltage signal > (well, actually, this is a slight oversimplification... but the exact method is > much more complicated to explain but gives the same danged result). Guess what? > No matter what the distance, it is at the _same_ place - when the sensor and > magnet are right over one another. End result? So long as the sensor isn't so > far away from the magnet that the signal is too weak to be seen, it really > doesn't matter. The Hall effect switches that I'm familiar with trigger at some magnetic field threshold. When the vector component of the field in the direction that the sensor responds to reaches this threshold the switch closes. Do the engine control HE sensors work differently? I suppose they could differentiate the signal and take the + to - zero crossing which would occur at the right place each time (right over the magnet.) Do you think they, including Pertronix, are this sophisticated? If this is what they do then I'll agree with you. If not, then we still have a problem or they do something else that I'd like to understand. > What _is_ important is the accuracy of magnet placement on the spinning > disc. Good mfg tolerances help. A large radius helps. Yes, the large radius point was my original one. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org